The present invention relates generally to molding apparatus, and more particularly, to improved apparatus and methods for molding rubber articles, or composite articles which include rubber and another, stiffer material such as metal, under conditions of great precision, high volume and low cost.
In one of its aspects, the invention is concerned with maintaining predetermined vacuum level within a so-called vacuum box surrounding a multiple cavity mold which is opened and closed by a large molding press.
Today, precise parts having molded rubber components, such as oil seals which include a rubber sealing lip and metal mounting flange portion, are made in large quantities by molding methods which are sometimes referred to as compression molding, transfer molding and injection molding. Commonly, compression molding involves simultaneously manufacturing a large number of articles in a mold having multiple cavities; such a method is often very economical because tooling costs, although high, may be amortized over long production runs. High unit production is possible because many parts are produced with each cycle of the press.
As rubber part manufacturing technology has become more refined, and the demand for precision-made products has heightened, a common concern in the industry has become the application of proper vacuum technology to such rubber molding. Evacuating the space within and immediately surrounding a rubber molding cavity has been found necessary and advantages for a number of reasons. First, unlike thermoplastic materials, rubber materials achieve their cross-linking or curing by undergoing an exothermic reaction which, in addition to heat, usually also produces gases of various kinds as a reaction product. Moreover, high temperatures achieved in cross-linking, vulcanizing, or curing of the rubber vaporize components which might otherwise be solid or liquid at lower temperatures.
Properly used, a vacuum applied to the interior of a mold cavity from the outside thereof helps speed the flow of fluent rubber into the cavity and insures complete filling thereof. This is particularly advantageous where it is necessary that voids, pock marks, inclusions or entrapments of air, gases or the like must be avoided in the finished product. From a theoretical standpoint, applying vacuum to a mold is fairly simple and straightforward, but in practice, it has often proved difficult to obtain and maintain a suitable relatively constant vacuum level in the vicinity of multiple cavity molds over a long period of time while maintaining a consistent vacuum level.
Thus, for example, applying individual vacuum lines to the interior of each individual cavity in a multiple cavity mold adds complexity, and often more than offsets the economies realizable by multiple cavity molding. Moreover, in view of the fluent nature of the rubber material before curing, individual vacuum passages often tend to become completely or partially clogged during use, with the result that vacuum is not effective or only partially effective in certain of the cavities.
In large presses adapted to receive multiple cavity mold parts, the mere physical size of the press also creates a problem of loading and unloading which is usually solved only by providing top or bottom plates, or both, which tilt or slide toward and away from the operator to facilitate loading and unloading. Provision of movable parts such as these further reduces the possibility that merely surrounding the mold area with a simple vacuum box will prove satisfactory in making precision parts. Provision of other parts having relative motion, such as lower or intermediate plates, strippers, and loading trays still further complicates simple and economical application of vacuum theory to existing press and mold designs.
According to the present invention, a system is described which provides ready access to all parts of the mold, which provides simple and easy loading and unloading, and which further provides for rapid isolation of the mold parts themselves from the surrounding atmosphere so as to draw an effective vacuum on a closed mold. Moreover, presses made according to the invention allow full access to the mold elements immediately upon opening the mold for removal of parts and for easy mold cleaning.
In the prior art, a number of vacuum systems have been proposed as suitable for use with molding presses. Many of these, however, failed rapidly in use because they were themselves the subject of increased loading placed thereon by the mold itself in undergoing opening, closing, and full clamping force modes of operation.
In view of the foregoing and other drawbacks of the prior art, and in view of the need for improved apparatus and methods for rubber molding, it is an object of the present invention to provide an improved vacuum arrangement for a molding press.
Another object is to provide a vacuum box assembly which is particularly adapted for use with large molding presses containing multiple cavity mold plates.
A further object is to provide a combination press and vacuum arrangement wherein high closing forces may be applied to the mold parts, but wherein deflection occasioned thereby does not adversely affect the structure or integrity of the vacuum box.
Another object is to provide an improved, highly flexible vacuum system for a molding press which is compatible with various movements of the molding press as well as movements of the mold plates and other parts thereof during use.
A still further object is to provide a vacuum apparatus which creates minimum wear on itself and on associated mold parts during use, and which may therefore be cycled repeatedly without damage.
A still further object is to provide a molding apparatus having a novel arrangement of moving parts, whereby the vacuum box arrangement may be opened and closed during cycling of the press to facilitate loading and unloading of the mold plates as well as improved operator convenience and safety.
A further object is to provide a novel mounting and movement system for a combination mold plate and vacuum box arrangement.
Another object is to provide an apparatus which, in use, permits movement of certain mold parts within the molding press to different positions of use while providing a safety device to prevent accidental damage to the movable mold plates or to an operator.
Another object is to provide a vacuum arrangement for a molding press which permits relative motion between molding parts and stripper elements adapted to remove finished parts from the mold, all without loss of effective vacuum in use.
Another object is to provide a vacuum box arrangement for a molding press wherein a part of the vacuum box may be placed in an initially stressed position or mounted such that high mold closure forces will not be transmitted to the vacuum box mounting but will be transmitted to the press frame instead.
The foregoing and other objects of the invention, including objects inherent therein are achieved in practice by providing a vacuum box unit which includes sidewalls surrounding mold parts in the closed position thereof, means for sealing the mold parts in relation to the vacuum box, means permitting access to the area lying at least partially within the vacuum box and means permitting movement of the mold parts between different positions, including positions lying partially outside the vacuum area. Certain other objects are also accomplished by providing a novel mounting means and method for certain of the components of the vacuum box, particularly the movable components thereof.
The manner in which the foregoing and other objects and advantages are carried into practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout the several figures.